Wait, are you asking how to eradicate majano anemones or aiptasia anemones, or both?
Peppermint shrimp WILL NOT eat majano anemones or larger aiptasia specimens. If aiptasia is your issue, you'll still need to use a manual method to kill the larger anemones, while the shrimp should eat the babies. Keep in mind that its a 50/50 chance that your peppermints will eat aiptasia. Once they learn that other food is readily available (such as fish food), mist stop scavenging for aiptasia.
Unfortunately, there aren't many safe critters for majanos, they need to be eradicated manually.